1. Field of the Invention
The present invention is directed to hand held and table top grinders and homogenizers such as those used to release proteins and nucleic acids from biological samples and those that grind geological samples for composition analysis. Samples may include, for example, seeds, soil, bones, teeth, tissues, spores, yeasts, and gram positive microbes. Certain embodiments, described below, result in more efficient and faster processing of said samples.
The most commonly used homogenizers are of the bead mill type (bead-beater), in which a biological or geological sample is added to a container such as a sample vial or tube that is preloaded with grinding media such as, but not limited to, for example, ceramic, glass or metal beads. A special buffer designed to dissolve proteins, nucleic acids, minerals and/or metals may also be added, followed by sealing of the tube typically with a screw cap. The sealed tube is then placed into the homogenizer, which mechanically agitates it in an oscillatory manner, causing the media (hard beads) within the tube to impact and break the sample. Typical rates of oscillation are in the range of 4,000 to 5,000 cycles per minute. This grinding or homogenization of the sample facilitates the extraction of proteins, nucleic acids, metals and/or minerals for use in downstream processes such as amplification, analysis of DNA and/or analysis of metal/mineral composition.
The biggest drawback with most bead mill homogenizers is that their range of oscillatory motion is not high enough to cause the beads to traverse the whole length of the sample processing chamber such as a sample vial or tube. Furthermore, if the sample tube is oriented vertically in the homogenizer, gravity tends to cause the beads to localize at the bottom of the tube during homogenization. At the same time, the biological sample, which is less dense than the beads will tend to stay closer to the top of the tube. As a result, the time to achieve complete homogenization is long, usually in the range from 5 to 60 seconds; perhaps longer if the sample is also hard (e.g. dry corn kernel, bone, etc.). Another undesired effect from this inefficient homogenization scheme is the generation of heat proportional to the length of time of homogenization due to internal friction within the tube. This heat is problematic if the desired nucleic acids are RNAs, which quickly degrade at elevated temperatures.
The previously mentioned drawbacks could be mitigated if the amplitude of oscillatory motion were to be extended to be at least equal to the length of the tube being used to process a biological sample such as that in the apparatus of the present invention. Doing so would cause the milling beads within the tube to traverse the whole length of the tube, enhancing the incidence of encounters between the beads and the sample. This more efficient design of the apparatus of the present invention in turn results in shorter homogenization times and thus, less heat generation. The preferred embodiment of the present invention has substantially improved grinding/homogenization efficiency, leading to shorter homogenization times, and less heat generation compared to those in the prior art.
2. Description of Related Art
There are a number of bead mill homogenizers (bead-beaters) on the market including that disclosed in U.S. Pat. No. 5,567,050, entitled “Apparatus and method for rapidly oscillating specimen vessels”, which describes an apparatus and method for rapidly oscillating specimen containing vessels such as those used in an RNA recovery operation wherein small sized glass sized beads in the vessel are employed to disrupt the cell walls of an RNA component to release the RNA, includes a specimen vessel holder provided as a disc in which the containers are received. The disc is operably connected with oscillatory motion producing means that in operation oscillates the disc rapidly in an oscillatory movement up and down symmetrically of a fixed vertical axis. The disc is haltered so it cannot rotate about the fixed axis. Locking means in the form of a locking plate locks the vessels on the vessel holder and applies a clamping force thereto to prevent relative movement between the vessels and the holder to prevent generation of heat that could be of deleterious effect to the specimen material or the vessels holding same.
Another example of a bead beater is described in U.S. Patent Application Publication No. 20120263010, entitled “Device for the Quick Vibration of Tubes Containing, In Particular, Biological Samples” which discloses an appliance for rapidly vibrating test tubes containing samples to be ground up, the appliance comprising an electric motor for driving rotation of a disk that is provided with an eccentric pin, the appliance being characterized in that the test tubes are perpendicular to the eccentric pin and are held by a clamp mounted on a support that is substantially parallel to the eccentric pin, being connected to a fixed baseplate via a Cardan type hinge having two mutually perpendicular axes of rotation (X and Y), one of which axes (Y) is substantially parallel to the eccentric pin and connects the support to the other axis (X) of the hinge that prevents the support from moving in rotation about a perpendicular axis (Z). The support is connected to the eccentric pin by a link.
Both of the above devices produce a Figure 8 motion, with respective capacities of 12×2 mL and 3×2 mL sample tubes/vials, and peak to peak amplitudes of ⅝ and ¾ inch. Since the sample tubes/vials in both examples are 1.5 inches tall, this means that the sample and hard matrices do not have the opportunity to travel throughout the whole length of the sample vial and they stay mostly at the bottom of the sample vial. In contrast, the apparatus of the present invention produces an elliptical motion/path and has a peak to peak amplitude equal to the length of the sample vial (1.5 inches, for example) allowing the matrices to fully interact with the sample throughout the sample tube/vial (sample processing chamber), making it much more efficient, achieving the same results, as the devices above, in about 1/10th the time of the other bead mill/bead-beater homogenizers.
Table 1 below outlines characteristics of commonly used sample grinders and homogenizers, for example, including a preferred embodiment of the apparatus of the present invention showing the peak to peak amplitude advantage of the present invention. The peak to peak amplitude of the present invention is not limited to 1.5 inches but is shown only as an example. Peak to peak amplitude can be adjusted in the apparatus of the present invention to match the sample processing chamber (sample vial) length by varying the diameter of its crank to match the length of the sample processing chamber.
TABLE 1SampleFrequencyAmplitudeProductTypeActionthroughoutRange (cpm)(inches)PRESENT INVENTIONBead-Beatercrank-slider (combination of circular 1  750-4,4001.5and linear motion)XpeditionBead-BeaterVertical Linear impaction13,6000.25Tissue-TearorRotor-statorProbe Rotor-stator1 5,000-35,000not applicableShredder SG3PressureHydraulic forcing of sample through 1200not applicablea sieve with simultaneous rotational mechanical grindingDisruptor GenieBead-Beaterhorizontal orbital motion121,000-3,0000.5Bead-BugBead-BeaterArc-shaped trajectory (~2 inch radius)32,700-4,0000.75Mini-Bead beater-1Bead-BeaterArc-shaped trajectory (~2 inch radius)12,500-4,8000.75Bullet Blender (BBX6F)Bead-BeaterHorizontal Linear impaction24  100-1,2000.125TissueLyser LTBead-BeaterVertical linear motion12  900-3,0000.75PRECELLYS ® 24Bead-BeaterArc-shaped trajectory (~3 inch radius)246,5000.315MINILYSBead-BeaterArc-shaped trajectory (~3 inch radius)33000, 4000, 50000.63